This invention relates generally to fluid flow control devices and, more particularly, to a flow control damper having a curved extension plate which provides for linear control over the fluid flow rate for a wide range of damper openings.
The use of fluidized beds has long been recognized as an attractive means of generating heat. In this use, air is normally passed through a bed of particulate material, which includes a particulate fossil fuel, to cause the material to expand and take on a suspended or fluidized state. The basic advantages of such an arrangement include an increase in combustion efficiency, an improved heat transfer rate, a uniform bed temperature, combustion of the fuel at lower temperatures, and ease of handling of the fuel materials.
Also, when the heat produced by the fluidized beds is utilized to convert water to steam, such as in a vapor generator, still other advantages ensue, such as a reduction in corrosion and boiler fouling and a reduction in boiler size. However, in a vapor generator environment there is an inherent limitation on the range of heat input to the water passing in a heat exchange relationship to the fluidized bed, principally due to the fact that the quantity of air supplied to the bed must be sufficient to maintain the bed in a fluidized condition and yet must not cause excess quantities of the fuel material to be blown away. Therefore, the requirement exists for an air flow control device which will permit close control of the air flow to the fluidized bed.
Many flow control devices, such as dampers, are known in the prior art for regulating the flow of fluid through a passage. These dampers, however, have not proven entirely satisfactory for controlling the quantity of air supplied to fluidized beds since they have not been capable of providing close control of the air flow. Generally, an excessively large flow is established when the dampers are first opened and they do not provide the necessary close control of the effective, open, flow area as the damper opening is increased.